The objective of this research program is to determine the contribution of one-electron (1e-) and two-electron (2e-) oxidation to the metabolic activation of polycyclic aromatic hydrocarbons (PAH) to tumorigenic agents. In particular, 1e- and 2e- oxidation may account for the differences in activity observed for certain PAH between their potent carcinogenic activity in mouse skin and their relative weak activity as mammary carcinogens in rats. The research will perform comparative studies with a wide selection of structurally diverse PAHs which have been shown to differ significantly in their carcinogenic activity in target organs of rat organs of rat mammary gland and mouse skin. The formation of PAH:DNA adducts, as detected by 32P-postlabeling analysis, will be evaluated and employed as a parameter to distinguish between 1e- and 2e- oxidation of PAHs. In vitro systems will be used for the synthesis of reference PAH:DNA adducts indicative of PAH activation and binding to DNA following 1e- and 2e- oxidation. PAH:DNA adduct profiles obtained using in vivo systems will be compared to synthetic reference profiles to determine each pathways contribution to PAH activation and binding to DNA in vivo. Comparative studies with rat mammary gland and mouse skin will be performed using Sprague-Dawley and Long Evan rats along with Sencar and CD-1 mice respectively. Studies will also investigate the polymorphism of mammary carcinogenesis in the above rat animal models. These experiments will characterize individual differences associated with PAH:DNA adduct formation within a single stain of animals as well as determine the critical levels and/or patterns of PAH:DNA adducts which give rise to mammary gland tumors within an individual animal. The proposed studies will us conventional 32P-postlabeling methodology as well as additional analytical methods which will be developed in this research program. In particular, the development of a biopsy procedure for evaluating PAH:DNA binding in individuals animals, HPLC analysis systems compatible with 32P-postlabeling analysis, and a boronate chromatography procedures to distinguish between 32P-labeled PAH syn- and anti- diol epoxide:DNA adducts will significantly advance current methodologies.